Denis Boucher, a spokesman for the owners of the Cape Breton and Central Nova Scotia Railway, says an investigation is underway into what caused several cars carrying a mix of propane and butane to derail Monday.

The derailment happened in West River Station, about 150 kilometres northeast of Halifax.

Several nearby homes were evacuated.

Boucher says the derailment involved seven tanker cars â six of which overturned.

He says the company doesnât know how long it will take to clear the track and resume operations.

Finding out what caused the train to derail will take some time, Boucher said.

âWe really need to complete the investigation and then weâll be in a better position to say what happened,â he added.

The RCMP said residents of six homes that were within a 2.5 kilometre radius of the derailment were still awaiting word on when it will be safe to return.

Const. Bryce Haight said there is minimal risk of fire, but police needed approval from the railway, provincial regulators and the remediation experts before allowing the families to return.

Police said the trainâs engineer realized there was a problem and stopped the train, which was en route to Truro from Stellarton.

New Glasgow fire Chief Doug Dort said his departmentâs hazardous materials unit took readings at the scene on Monday.

âThere were no leaks detected when we left the scene last night,â said Dort.

Last month, three cars from a train carrying steel plates derailed on the same railway in downtown New Glasgow.